Fetal tissue, and in particular fetal DNA, is routinely used in prenatal diagnosis and other medical procedures which require an accurate assessment of the genome of the fetus. Currently, the fetal tissue is obtained by the use of aminocentesis, chorionic villus sample (CVS), fetoscopy, or cordocentesis, as described in Thompson and Thompson Genetics in Medicine, 5th Edition, W. B. Saunders Co., Phila., 1991).
In aminocentesis, a sample of amniotic fluid, which contains fetal cells, is transabdominally removed from the mother, with a needle and syrine. Aminocentesis has inherent associated risks. The major risk is induction of miscarriage which is estimated to occur at 1 in 200 amniocenteses. Other risks include material infection and physical damage to the fetus. In CVS, fetal trophoblast tissue is aspirated from the villous area of the chorion transcervically or transabdominally. The rate of fetal loss by this method may be as high as 1 in 100. Cordocentesis provides a method of obtaining fetal blood directly from the umbilical cord with ultrasonic guidance. Each of these invasive methods carries risks to both the mother and the fetus.
Accordingly, it would be desirable to have a non-invasive method for obtaining fetal tissue or fetal DNA. It would also be desirable to have a method for isolating and enriching the fetal tissue from material tissue that is rapid and reliable in order to facilitate screening and pre-natal diagnosis in clinical laboratories. It would also be desirable to have a method of isolating and enriching rare cells from a population of blood cells. Surprisingly, the methods of the present invention accomplish these and other related needs.